Present designs for many generator stator cores consist of a multitude of individual laminations secured together to form the core. In large generators, this involves the use of several thousand laminations to form the core. To satisfy electromagnetic requirements, these laminations are typically made of iron or thin silicon steel. It is essential that these laminations be tightly clamped against each other so as to resist the fluctuating magnetic forces imposed on them during generator operation.
The required clamping force is generally provided by elongated through-bolts or studs which run the length of the core. These studs are uniformly distributed around the circumference of the core, or about the center of pressure of the stator core area. As an aid to evenly distribute the clamping force of the through-bolts over the area of the laminations, devices referred to as fingerplates are utilized. The fingerplates are segmented structures completing a full circle on the end of the core, there being typically eight (8) segments at each end of the core. The fingerplates are usually riveted to the first layer of laminations at each end of the stator core. Riveting serves to locate the fingerplates accurately relative to the laminations.
Adjacent the fingerplates, on the side opposite the laminations of the core, high conductivity endplates are also held in place by the through-bolts passing therethrough. These endplates are typically made of aluminum or copper, and are of one-piece construction. During operation of the generator, heavy electrical currents circulate within the high conductivity endplates. These currents divert end region magnetic fringing flux away from the flat surfaces of the ends of the stator core. Theses currents heat the endplates, causing them to be hotter than the core to which they are secured. The combination of the temperature differentials and differences in thermal expansivity between endplate and core, due to their being constructed of different materials, result in relative thermal expansion and contraction between the endplates and stator core during generator load changes. During these thermal expansion and contraction cycles, the endplates must be guided radially relative to the fingerplates to preserve original concentricity of the endplates, fingerplates and the core.
One such design used to accommodate this relative thermal expansion and contraction includes radial guide pins which are inserted through round holes in the endplates into radial guide slots which are fixed to the fingerplates. These radial guide slots are presently machined into blocks which are welded to the fingerplates after the core laminations have been stacked, the endplates placed, and the through-bolts inserted and tightened. This arrangement is necessary because the fingerplates and endplates cannot be aligned closely enough to permit direct insertion of the guide pins through the holes in the endplates and into radial guide slots. This in situ welding gives rise to manufacturing difficulties, due to the rather tight location within which the guide blocks are welded. Additionally, sizing and positioning of the guide blocks are difficult when working in such a limited area. Close alignment is required, to insure that the movement between the endplates and the core due to the relative thermal expansion is provided for.
It is therefore an object of the present invention to provide an alignment device for between a generator stator core and associated endplates which obviates the need for welding operations after the core has been assembled.